1. Field of the Invention
The present invention relates to a side view Light Emitting Diode (LED) package in use with an LCD backlight unit. More particularly, the invention relates to a side view LED package having a lead frame structure designed to improve resin flow in order to ensure stability even if the LED package is made extremely thin.
2. Description of the Related Art
Side view LEDs are widely used as a light source of a backlight unit of a small-sized LCD in a mobile phone, a Personal Digital Assistant (PDA) and so on. The side view LEDs are used in a package, in which their mounting height is getting gradually reduced and it is expected that a dimension of 0.5 mm or less will be required. Furthermore, the LED package should ensure high reliability while realizing high brightness by minimizing light loss and so on.
At present, in order to reduce the thickness of the side view LED package, endeavors have been made to reduce the thickness of upper and lower wall parts around an LED window. However, reducing the wall part thickness is extremely difficult task. This task also potentially weakens wall strength thereby failing to ensure reliability.
This will be described in more detail with reference to FIGS. 1 to 4, in which FIG. 1 is a front elevation view of a general side view LED package, FIG. 2 is a cross-sectional view illustrating resin flow on a plane taken along the line II—II in FIG. 1, FIG. 3 is front elevation view of a side view LED package having lead frames of the prior art, and FIG. 4 is a cross-sectional view illustrating resin flow on a plane taken along the line IV—IV in FIG. 3.
First, strip-shaped lead frames 40 are disposed in a mold as shown in FIG. 2, and resin is injected into the mold, such that resin forms a body 12 and a wall 14 surrounding a cavity C of an LED package 10 during the flow along the direction of arrow A. Resin spreads laterally in a rear half 12b of the body 12 about lead frames 40, and then directs toward a front half 12a of the body 12. In the meantime, upper and lower wall parts of the front half 12a of the body 12 are formed of resin that flows over the lead frame 40 as indicated with arrow B.
As shown in FIGS. 2 and 3, the lead frames 40 are placed along substantially the entire length of the LED package 10, with a width larger than that of the bottom 16 of the cavity C. That is, as shown in FIG. 4, the lead frames 40 are spaced from the outside surface of the body 12 at a small gap 20, which acts as a bottleneck. Therefore, it is apparent that resin does not smoothly flow along the direction of arrow B.
Then, resin insufficiently feeds to central leading ends of the upper and lower wall parts 18, thereby creating molding defects such as V-shaped voids.
In particular, since the LED package is getting longer in reverse proportion to its thickness reduction, the central leading ends of the wall parts 18 become more susceptible to molding defects.
In the meantime, heat generated from the operation of the LED chip 30 expands the lead frames 40 inside the LED package 10 along the length of the package 10. However, the lead frames 40 having different expansion coefficient from the package body 12 and an encapsulant inside the cavity C causes stress to the whole LED package 10 including the lead frames 40.
Such stress if repeated or continued may cause the lead frames 40 to get loose or separated from the package body 12 to such an extent that a disconnection A takes place between a wire W and a lead frame 40 or between the wire W and an LED chip 30 as shown in FIG. 5.
These problems are getting more serious according to the reduced thickness of the LED package 10 accompanied with its increased length.